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# Geometrical Optics: refraction and reflection

Transcript

Hi guys today I'm going to show you that science is not only labs and the interesting things that we can do with so many little things. So now, what do we need to carry out this experiment? We need some milk, matches a glass of water and a laser pointer.

Firstly we're going to try viewing the way of the light from the water. Well to see propperly the experiment we're going to switch off lights. Unfortunately we can´t see the way of light throughout the water but if we add some milk it could be totally different. Only a little bit remember it
We have to remove as well. Now we can see without problems the way of light throughout the water with milk because the milk is an obstacle for the light of the laser.

On the other hand, secondly if we switch on the match and we keep the fume of the match inside, we can see now something incredible, awesome, is that the light is changing its direction when it arrives at the fume and if we change the angle of the light it could be totally reflected as well.

When light arrives at the media of different indexes of refraction, different density or different speed its direction changes. This phenomenon is known as a refraction. But light can be reflected as well with high angle in this case this phenomenon is known as total reflection. Snell`s law says it and relates the angle to the normal to the indexes of refraction.

Well guys this is all for today and remember:with the small things you can become the biggest scientist

THE LESSON STARTS!!

After this video related to a listening/comprehension task our students were supposed to do in a previous lesson, on this lesson our CLIL students will carry on with different tasks where they will have to show the teachers and their peers everything they have learnt about this topic and ...what betther to do it, than buiding up their own designs!

WHAT SHOULD BE TAKEN INTO ACCOUNT?

At the end of this lesson, the student should be able to:

- Explain how different media affect the transmission/reflection of waves travelling from one medium to another

- Recall that, in general, waves are transmitted and reflected at an interface between media.

- Discuss how scientific ideas may change over time, for example, our ideas on the particle/wave nature of elect

For being succesful in the subject, the students need to:

- Show propper English skills.

- Participate in the peer presentations, giving own opinions with appropriate English expressions but respectfully.

- Work in groups showing good knowledge of the matter.

ARE THERE ANY MATHS REQUIREMENTS?

Trigonometry

There is a unique relationship between the angles within a right triangle and the ratio of the length of the sides. Trigonometric functions are mathematical functions which relate the length of the sides of a right triangle to the angles within the triangle

In Physics, there are numerous physical situations in which a student would want to relate the angle in a right triangle to the length of one or more of its sides. In such instances, a trigonometric function is chosen and used to analyze the physical situation. For instance, the refraction of light at a boundary causes the angle that the light path makes with the normal (and also with the boundary) to change. Working close with the maths department is essential, so previous work with at least the most important math terms in CLIL lessons, such as : angle, degree, sum, multiply, divide, take away, plus, times or minus, will be helpful.

HOW WILL THE LESSON BE CARRIED OUT?

At the end of the previous lesson we can foster our class to make some research about anything related to the video watched as a part of the flipped lessons. This could go over the tough topic we mentioned before: Is light made of only one beam? They can work in groups of 5 and expose their 5 minutes- presentations the next lesson, which could be made in power point or in Prezi instead. That would be a great peer assessment, so they will realize about their own mistakes, both in content and communication, by correcting their own peers. The duration of this activity would be around 30 minutes.

Finally, a last but not least important thing are the quick practicals which can be carried out in the last half an hour of this second lesson. Four tables with four different easy experiments could be set up in the corners around the classroom and a person in charge (one of the students) will explain the practical designed to their classmates. Obviously, this experiments will be related to refraction and internal reflection of light. For instance, two of them could be over movement of light in different pieces of glass, another one over refraction in “weird” papers (cellophane) and even another one over a topic already seen in a previous topic: the diffraction of light by a piece of hair with a laser pointer.

Support: Students in charge may need help explaining the practical to their peers so they could have a list (the glossary) which they made during the first lesson as well as a list of interesting introductory phrases (Firstly…, Secondly…, for carrying out this practical we need…, what do we need to carry out this experiment?...)

Stretch: Ask students to list the similarities and differences between diffraction, reflection and refraction within the experiments done. By this way, they will get more fluency using comparison terms (compared to, I have the impression when comparing the two experiments that…light is refracted as the angles of refraction is bigger/smaller than the angle of incidence…whereas in reflection, the angle of incidence is the same as that of reflection… will be useful for other CLIL subjects too.

Expected results

Students model the Sunlight through air, water and glass.

Safety

Two characteristics of laser light contribute to the hazard:

• Laser light can be emitted in a tight beam that does not grow in size at a distance from the laser. This means that the same degree of hazard can be present both close to and far from the laser.
• The eye can focus a laser beam to a very small, intense spot on its retina, which can result in a burn or blind spot.

Equipment

Laser pointer, glasses with different index of refraction, cellophane, play-do, a piece of hair, card board with a hole, metallic cable and adhesive tape.

HOW WILL OUR STUDENTS BE ASSESSED AFTER THIS LESSON?

- The teacher will mark the student presentations evaluating grade of language, keywords used, fluency, content and participation correcting mistakes and giving other points of view on other groups presentations.

- The peers will evaluate each other (not only giving them a mark but giving them different perspectives). Nevertheless, the peer assessment will be taken into account by the teacher but only for positive points, which will scarcely affect their final marks (they could get better marks but never worse).

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